A late-night fire raced through a multifamily home, killing two young siblings, a 6-month-old and a 3-year-old, and injuring their pregnant mother and three other adults. The roof of the home in Putnam, in northeastern Connecticut, was engulfed in flames when firefighters arrived at about 1 a.m. Tuesday, and it later collapsed into the third floor, where the children were, authorities said. The bodies of the two dead children were found Tuesday afternoon. State Police provided their ages, but their names and other details were not provided. Fire investigators were trying to determine the cause of the blaze.